1. Field of the Invention
This invention relates generally to a fluid control valve and, more particularly, to a balanced pulse-width solenoid control valve that includes a star-shaped armature stop to minimize hydraulic tension between the armature stop and the armature.
2. Discussion of the Related Art
Modern vehicles generally employ an automatic transmission controller that includes several solenoid operated fluid control valves that independently act to control the pressure of the transmission fluid in the vehicle's transmission to operate various components of the transmission. For example, solenoid operated fluid control valves are known that use transmission fluid pressure to provide direct clutch control and line pressure control applications. The torque transmitted by a transmission clutch may be varied by varying the pressure of engagement between opposed clutch plates. Presently available transmission controllers can rapidly and precisely generate the desired electrical output to operate the control valves in response to sensed vehicle operating conditions to provide this pressure.
One particularly known solenoid valve used for this purpose is referred to as a balanced pulse-width modulated (PWM) solenoid valve, well known to those skilled in the art. The pulse-width modulated solenoid control valve is typically used to supply a hydraulic control pressure proportional to the duty cycle of a pulse-width modulated driver signal. The control pressure is provided that is a linear relationship to variations in "on-time" of the solenoid coil. The control valve that controls the fluid connection of the control port to a pressure supply must be capable of rapid shifting in close synchronization with the energization and deenergization of the coil. In order to effectively provide this transmission control, the pulse-width modulated solenoid control valve should prevent occurrence of oscillations due to the natural frequencies in the system, and smooth the pressure pulsations. The frequency of operation of the control valve is typically in the range of 30-100 Hz. Additionally, the valve seats must be capable of withstanding up to 1.5.times.10.sup.9 switching operations at this frequency.
In certain solenoid control valve designs, an armature moves axially within the valve to open and close hydraulic ports within a valve body. When the armature moves from one position to another position, it will seat against an upper or lower armature stop. U.S. Pat. No. 5,076,326 issued to McCabe Dec. 31, 1991 discloses a control valve of this type. The armature should be movable in response to a relatively small magnetic force in order to minimize the size and power requirements of the control valve. When the armature is seated against an armature stop, hydraulic tension or vacuum locking between the armature stop and the armature sometimes adversely interferes with the ability of the armature to move from one position to another in close synchronization with coil energization and deenergization. The McCabe valve attempts to minimize this effect by forming depressions in the ends of the armature to minimize the surface contact between the armature and armature stop. U.S. Pat. No. 4,917,150 issued Apr. 17, 1990 to Koch et al. also includes this feature. However, this type of machining of the armature adds significant expense to the cost of the valve.
As the automatic controllers become more sophisticated, it is necessary that the solenoid operated control valves also include advancements and improvements over the state of the art. In this regard, it becomes important to increase the operating efficiency, reduce the cost, reduce the weight, reduce the complexity, etc. of the existing solenoid operated fluid control valves. Therefore, advancements in part reduction, component simplification, increasing valve stroke, etc. of the control valves is advantageous.
It is one object of the present invention to provide a solenoid control valve that further minimizes hydraulic tension between the armature and armature stop in a cost effective manner, and includes other advancements over those control valves known in the art.